The webinar launched in the frame of SOPHi@Webinar and 7FP-CHEETAH project concerns the introduction to the procedure based on the transfer-matrix method (TMM) utilized @ HZB to extract optical parameters in thin film for PV. The procedure is available in request

Useful information

Abstract

The refractive index of a material is not directly accessible to experiments, yet it can be extracted using optical measurements of transmission T and reflection R of a thin layer. Often times this extraction is performed based on physical models that need to be chosen carefully according to the specific material type. During the webinar, however, the speakers presented a procedure based on the transfer-matrix method (TMM) that allows the exclusive mathematical recalculation of the complex refractive index (n,k) from measured (T,R). The extended model cannot only be applied to flat thin films but it can also address common imperfections of thin layers like surface roughness or internal roughnesses (voids), which usually destroy the applicability of the TMM. The according simulation tool RefDex, which was developed based on this procedure, is very useful particularly for the characterization of multilayer stacks including roughnesses

Details

Unlike other physical parameters the refractive index of a material is not directly accessible to experiments. Yet, we can use optical measurements of transmission T and reflection R of a thin layer to extract its dielectric function. Often times this extraction is performed based on physical models that need to be chosen carefully according to the specific material type. Here we present a procedure based on the transfer-matrix method (TMM) that allows the exclusive mathematical recalculation of the complex refractive index (n,k) from measured (T,R). This means no particular material model for the film investigated is required. Moreover, we will address common imperfections of thin layers like surface roughness or internal roughnesses (voids), which usually destroy the applicability of the TMM, by adapting the model to consider these properties. By comparing (T,R) calculated as a function of the desired optical constants (n,k) with the measured data in an iterative minimization process of the deviation the desired dielectric function becomes accessible. This procedure under consideration of surface and internal roughnesses for a multilayer stack of thin films and thick substrates as well as with the option of an effective medium is possible via our simulation tool RefDex.